Life changes in the instant, wrote the American author, Joan Didion. You sit down to dinner and life as you know it ends.

It was Aoife Beary's 21st birthday. She and her friends, Olivia Burke and Eimear Walsh, were having a party in the apartment they were renting for the summer in Library Gardens, Kittredge Street, an accommodation block used by the University of California. Aoife was from Blackrock. Her friends were from Foxrock. They'd all gone to Loretto College. Their extended network of south Dublin friends, former classmates and college buddies were two weeks into the annual J-1 summer exodus of students to the US.

The party wasn't just about Aoife's birthday. One of the group, Conor Flynn (22), a DIT student from Mount Merrion, later told the Minister for the Diaspora Jimmy Deenihan, from his hospital bed, that they were also planning their holiday, things to do, places to see over the long hot summer ahead. "They all knew each other. Conor was saying that today, how they were all so close," said the minister.

Not everyone went to the party. Some students later told a priest, Fr Aidan McAleenan, that they had just got jobs and had to get up the next morning, so they didn't go. There was music and beer. Students wandered on and off the small balcony. Some of the neighbours weren't too happy with the noise. Two minutes after midnight, one neighbour phoned the Berkeley police to complain.

Police logged the call, and they would have gone to break up the party - the police station is just a short walk from the Library Gardens apartment block - except that somewhere across the city someone fired a gun. At 12.06am someone called the police to report the gunfire. Mike Meehan, the chief police officer, later said the shooting took priority.

The students continued to party. Minutes ticked by. Banal split- second decisions made in those last moments of normality marked the difference between life and death.

"So one young guy just went off to the jacks, I mean it was as simple as that. One [went] to the bar to get a drink. It was that momentary decision that saved their lives really," said Fr McAleenan, an Irish priest in San Fransisco who comforted survivors at John Muir hospital.

Shortly before 12.41, the wood beams supporting the balcony apparently snapped. The balcony and the railings flipped on to the balcony beneath, throwing the 13 students on to it and around 40 feet to the street below. According to the reports, the loud bang, not the screams, woke other residents.

The students on the balcony didn't stand a chance. "It wasn't a failure where you can start seeing it happen, where you can react, you can try and run off of it," James T Passaglia, a structural engineer in San Fransisco told RTE.

According to accounts given to Fr McAleenan, there was a split second when the students realised what was happening and their friends tried to pull them off.

"Speaking to several of them [the students], some of them got hurt by trying to pull the others in and got pulled out, is my understanding of what has happened. There are some really terrible stories that some of them tell," said Fr McAleenan.

Jack Halpin (21) from Rathmines, a UCD student and Gaelic footballer, grabbed his friend Clodagh Cogley (21). Both fell to the street below, both miraculously survived. From her hospital bed, Clodagh later credited Jack with breaking her fall.

Students raced downstairs to the broken bodies of their 13 friends lying on the street. Police came two minutes later, to a scene of students kneeling beside those who were dead or injured, holding their hands, doing what they could.

"It was unreal. I started going to all the bodies close by me to see who was breathing, who was not, who was reacting. We were looking to see who was alive and give them the appropriate help as necessary," an anonymous first responder told The Irish Times on Friday.

"There is a sense of horror at what you are seeing combined with a sense of helplessness. That's what you had here," said police officer Jeff Shannon, a mental health professional who has counselled some of the police officers at the scene.

"Medical staff got there very quickly, but the officers there did an amazing job in stepping into a role we don't usually step into, which is triage," he said. All they could do was offer comfort: "I can't fix you medically, but I can be here with you."

"Their goal at that point is first aid and to get treatment and get everybody on the ambulance as fast as possible, hopefully to save as many lives as possible," said police sergeant Mary Kitmuss.

Four were pronounced dead at the scene, their remains opportunistically photographed as they lay on the street wrapped in body bags, waiting to be removed to the city mortuary. The Star's decision to publish the images was widely criticised.

The injured students were rushed to the city's three hospitals - Highlands in Oakland; Eden Medical Centre and John Muir Medical Centre, where a fifth student and then a sixth were later pronounced dead.

Eimear Walsh, a medical student in UCD, died of her injuries. She was from Foxrock. So did her school friend and flatmate, Olivia (21). Olivia was studying entrepreneurship and management at Dun Laoghaire Institute of Art, Design and Technology.

Ashley Donohue (22), Olivia's American cousin, also died. She lived in Ronhert Park, Sonoma County, north of San Francisco, where she studied biology at university. She wanted to be a forensic pathologist. Her parents emigrated from Dublin in the late 1980s.

Three young men died. Niccolai Schuster (21) from Terenure in Dublin impressed the American bar tenders where he worked with his "passionate" and "engaging" nature and his "contagious smile". He was a grandnephew of the Kerry playwright John B Keane. His father's mother was John B's sister, Peg.

He went to St Mary's in Rathmines with Eoghan Culligan (21) from Rathfarnham, who also died. Eoghan was six foot three and a "bundle of fun", according to the chairman of St Enda's GAA club where he played. He was a student at DIT.

Lorcan Miller (21), from Shankill, was an "outstanding student" with "amazing ability," according to his former headmaster at St Andrews. He was a third-year medical student and the eldest son of Ken and Sinead Miller.

There were many interconnections. Conor Flynn (22), who was one of seven students injured, played football for Bushy Park Rangers with Niccolai Schuster, whose dad managed the side. He and his friend, Jack Halpin (21), were sent to John Muir hospital, with broken limbs and back injuries.

Sean Fahy (21), another classmate of Niccolai's and Eoghan's at St Mary's College, Rathmines, was sent to Eden Medical Centre. Clodagh Cogley (21), also injured in the tragedy, is from Milltown, a psychology student in Trinity College and a grand-daughter of the legendary sports commentator Fred Cogley. Niall Murray (21), a student at University College Galway, was also injured.

The most seriously injured of the survivors are Hannah Waters (21), a Dublin City University student from Castleknock, and Aoife Beary. Both remained in a critical but stable condition in the Oaklands hospital this weekend.

At John Muir hospital, where Jack Halpin and Conor Flynn were being treated for serious injuries, Fr McAleenan, based at St Columba's parish in San Francisco, turned up, having heard of the tragedy.

"We were there with the nine young fellas, young lads that were friends of Conor and Jack, those two that were in that particular hospital. They were among the survivors. But we also had to tell one of them that his best friend had passed away, because he was the sixth one. That was hard-going because . . . when you tell somebody like that it's just, it's just very hard, all you can do is hold them and sort of cry with them. There are no words can help that," Fr McAleenan told RTE on Friday.

"They didn't know what to do with themselves. Twenty-year-old lads are not great at communicating the emotions. We were there for them, some of the representatives of the hospital, the first responders, were trying to get them to talk, but they just wanted to be with one another."

More than 8,000km away and eight hours ahead, the families of these students awoke to a sunny morning in Dublin. Many were probably at work or preparing for work, dropping kids to school, or doing some other mundane task that is part of the comforting rhythm of family life. Many of them heard that something had happened through the distraught messages flooding in on social media from their children, who were sending out distress calls from San Francisco in the early hours of the morning, shocked, traumatised, unclear who was dead and who was injured.

"The families are so interlinked," said Fr Frank Herron, who is a parish priest in Foxrock. "Their children would have gone to junior school together, then secondary school and then to UCD or to Trinity, he said. "So the parents often would gather together, driving children to football or to rugby or to tennis, there is a huge interlinking of the parents of that age group."

Parents rallied, contacting each other, gathering in each other's homes, to make the harrowing phone call to find out which of their children would be coming home. Over the following hours, parents of six dead students, of the seven injured and of others who were traumatised witnesses of the catastrophe, prepared to make the grim trans-Atlantic journey to claim their children.

Embassy officials were at the airport to meet them. The parents of dead children were brought straight to a support centre, set up at Berkeley City Hall, where the police station is based. Fr McAleenan said: "They are kind of running on empty. They are coming into a large room, a lot of strangers, so it was . . . They had to be debriefed on what the next steps were and all of the practical implications. We started off with a prayer and then went into the practical details of what they had to do."

The luckier ones went straight to the hospitals to keep bedside vigils by their children. Hannah Waters' father, Martin, told The Irish Daily Mail of his "long, long wait" to get there: "She's in and out of consciousness but she knows we are here. She is drifting in and out. But she was awake at times and we were able to get a few words."

In the aftermath of the carnage, the behaviour of the Irish J-1 students put the lie to the much criticised New York Times article, published the day after the tragedy that segued insensitively from the deaths of six students to drunken Irish J-1 student parties. Students rushed between hospitals, providing names, phone numbers and details of their dead and injured friends. They helped bereaved parents retrieve their children's belongings.

"The support they have shown for each other and for the families. They set up teams. We have them running in a shuttle between the different hospitals, just so everybody knows those who need our support," said Philip Grant, honorary consul in San Francisco.

On Tuesday night in Foxrock, the church doors swung open, the funeral bells rang, and people young and old, streamed in all night in an impromptu gathering. "Musicians turned up, though nobody had asked them to. A table appeared. There were candles by the millions. It was an extraordinary impromptu event," said Fr Herron. Similar scenes were replicated across the city, in St Mary's College in Rathmines, and in Castleknock, where the community has been praying for Hannah Waters' recovery. She and Aoife Beary remain the most seriously injured. The others are expected to make a full recovery.

The impact of the tragedy has reverberated far beyond the communities these children came from, as evidenced by the vigils, the memorial services, the fundraising and outpourings of support.

As the Dail prepared to hold a minute's silence last week Taoiseach Enda Kenny, rose and said: "When you look at the newspapers this morning, don't you see your own children?"

Even in this dark time, the parents of six dead children somehow found it in themselves to tap into this spirit of empathy. Olivia Burke's parents brought her to her cousin Ashley's home town. Ashley was laid to rest and Olivia continued on for the journey back to Ireland, along with her four deceased friends, Niccoli, Eoghan, Eimear and Lorcan, an act of solidarity.

"They are consoling each other, comforting each other and finding solace in each other's company," said Mr Deenihan. "They are the only ones who can really understand the depth of the pain they are going through."